How to solve problems on concentration

How to solve problems on concentration

Concentration is a relative maintenance of a certain component in more complex structure. As a rule, concentration of any given substance is defined in solutions or mixes of various substances. In the molecular and kinetic theory understand quantity of molecules of gas in unit of volume as concentration.

It is required to you

  • - solutions of different concentration;
  • - water;
  • - calculator.


1. To find concentration substances dissolved in water use a concept of mass fractions of these substances. For this purpose put the mass of water and substance which in it is dissolved. After that divide the mass of the dissolved substance into the mass of solution, and increase result by 100%. The turned-out number will also be concentration of substance in solution. For example, if in 200 g of water to add 50 g of table salt, then we will charge 240 g of solution. Divide the mass of salt into the mass of solution and increase by 100% (50∙100/240=20). Concentration of table salt in solution makes 20%.

2. To solve a problem on change of concentration, the beginnings find the mass of solution which has to be at change of concentration with this mass of the dissolved substance which find, using data on the mass of solution. After that calculate how many solvent needs to be added to it. For example, concentration of sugar in 160 g of solution is equal to 20%. How many it is necessary to add waters that concentration of solution became 10%? Determine the mass of sugar in solution for this purpose the mass of solution increase by concentration of substance and divide into 100%, receive 160∙20/100=32 g. To receive solution concentration of 10%, its lump has to be 32∙100/10=320 g. For receiving 10% of solution add 320-160=160 more g of water.

3. As concentration of molecules of gas is equal to their quantity in unit of volume that to find it, divide quantity of molecules of gas N, into the volume of V which they occupy n=N/V. If there is no such opportunity, then for definition of concentration use one of the investigations of the main equation of the molecular and kinetic theory. To find concentration of molecules of gas, divide its pressure upon Boltzmann's constant k=1.38∙10^ (-32) and the gas temperature taken in Kelvins of n=p / (k∙T).

Author: «MirrorInfo» Dream Team